Influence of three-body forces on the gas-liquid coexistence of simple fluids: The phase equilibrium of argon

The effect of three-body classical dispersion forces on the gas-liquid coexistence of argon is explored by means of a reference hypernetted-chain integral equation and Gibbs ensemble Monte Carlo simulations. We find that the combination of Aziz's [J. Chem. Phys. 99, 4518 (1993)] pair interaction with the standard Axilrod-Teller [J. Chem. Phys. 11, 299 (1943)] triple dipole potential leads to the best prediction of the experimental coexistence curve. By contrast, when the Lennard-Jones potential is used in conjunction with the Axilrod-Teller interaction the calculated curve deviates appreciably from the experimental data, far from improving the reasonable plain Lennard-Jones results. Additionally, the integral equation approach with an effective state-dependent pair potential to account for the three-body interactions leads to very accurate results for the thermodynamic and coexistence properties of the fluid. This feature comes to prove that the theory can be an invaluable tool for studying systems with three-body interactions of the Axilrod-Teller type.